The present invention generally relates to optical disc recording apparatuses, and more particularly to an optical disc recording apparatus which records a frequency division multiplexed signal of a frequency modulated luminance signal and a frequency converted carrier chrominance signal on an optical disc by use of a laser beam.
Conventionally, there are known recording apparatuses which record and reproduce a video signal on and from an optical disc by use of a laser beam generated from a laser diode. In one type of recording apparatus, a frequency division multiplexed signal is recorded and reproduced from the optical disc, where the frequency division multiplexed signal is obtained by frequency-division-multiplexing a frequency modulated (FM) luminance signal and a frequency converted carrier chrominance signal which has been frequency-converted into a frequency range lower than that of the FM luminance signal. In this type of recording apparatus, a current dependent on a level of the frequency division multiplexed signal is supplied to a laser diode which generates the laser beam at the time of a recording, so that a maximum value of the laser power is obtained at a maximum value of an envelope of the frequency division multiplexed signal and a minimum value of the laser power is obtained at a minimum value of the envelope of the frequency division multiplexed signal.
However, the envelope of the frequency division multiplexed signal varies depending on a level of the frequency converted carrier chrominance signal. For this reason, the envelope of the frequency division multiplexed signal has an intermediate value between the maximum and minimum values. But it is difficult to obtain the laser power corresponding to this intermediate value of the envelope of the frequency division multiplexed signal, and it is thus difficult to make the laser power setting for an optimum recording.
In addition, a relative linear velocity between the optical disc which rotates at a constant angular velocity and the laser beam which scans the optical disc becomes smaller toward the inner periphery of the optical disc. But although an amplitude of a reproduced FM luminance signal becomes smaller as the relative linear velocity becomes smaller, an amplitude of a reproduced frequency converted carrier chrominance signal remains virtually unchanged.
Therefore, in the conventional recording apparatus which records the frequency division multiplexed signal on the optical disc with a constant mixing level ratio (multiplexing level ratio) between the FM luminance signal and the frequency converted carrier chrominance signal throughout the entire recording region on the optical disc, a mixing level ratio of a reproduced frequency division multiplexed signal changes at the time of a reproduction depending on a radial scanning position on the optical disc. As a result, there is a problem in that the quality of the reproduced picture which is obtained from the optical disc at the time of the reproduction changes depending on the radial scanning position on the optical disc.